| Abstract|| |
Context: Brain metastases are the most common intracranial neoplasms. They are often the first symptom of systemic malignancy. Hence, immunohistochemistry (IHC) is of importance in evaluating the origin of brain metastases. Aims: The aim was to detect the primary site of brain metastases and evaluate the role of IHC in diagnosing the same. Materials and Methods: Data of 74 patients of brain metastases with unknown primary was analyzed. IHC was performed in these cases. The histopathological findings were correlated with clinical and radiological data. Results: Of 74 cases in which IHC was done; the most common primary site was lung (51 cases). Even after applying IHC, the primary could not be diagnosed in 10 cases. Conclusion: Brain metastases are often the first indicator of systemic malignancy. Lung is the most common primary site in cases with unknown primary, as deduced by IHC findings.
Keywords: Brain metastases, immunohistochemistry, unknown primary
|How to cite this article:|
Sharma P, Trivedi P, Shah MJ. Evaluation of central nervous system metastases with immunohistochemistry correlation. Indian J Pathol Microbiol 2014;57:376-9
|How to cite this URL:|
Sharma P, Trivedi P, Shah MJ. Evaluation of central nervous system metastases with immunohistochemistry correlation. Indian J Pathol Microbiol [serial online] 2014 [cited 2019 Aug 23];57:376-9. Available from: http://www.ijpmonline.org/text.asp?2014/57/3/376/138719
| Introduction|| |
Brain metastases are the most commonly encountered intracranial tumors.  It is estimated that 10-15% of patients with cancer will develop metastases involving the brain during their lifetime.  Of metastatic tumors involving the central nervous system (CNS), 60-80% are due to primary tumors arising, in decreasing order of incidence, from the lung, breast, skin (melanoma), colon, and kidney, respectively.  The large majority of metastases arise from carcinomas, and studies have shown that approximately a third of these carcinomas are unrecognized before their metastasizing to the brain. ,
After obtaining a brain biopsy specimen, which confirms the presence of metastatic carcinoma, a thorough and costly search is often undertaken to identify the likely primary site. Even after a search for the primary is performed, the source of the metastasis may remain unidentified in 16-48% of cases, with lung primaries being especially difficult to detect. ,
Traditionally, the pathologist's strategy with brain metastases specimens has been to first determine that they are not high-grade glial neoplasms, followed by a simple diagnosis of "metastatic neoplasm" or "metastatic carcinoma." This strategy likely developed over time for several reasons. For many years, the diagnosis of carcinoma was based on hematoxylin and eosin-stained sections and routine stains such as mucicarmine may have suggested adenocarcinoma, but no further definition was possible. With IHC in the 1980s, it became possible to demonstrate cytokeratin (CK) immunoreactivity in metastatic epithelial neoplasms.
However, it was not possible to define the possible site of origin for these tumors. The introduction of markers such as carcinoembryonic antigen (CEA) and B72.3, which were heralded as revolutionary markers for gastrointestinal tumors and breast malignancies, added to this frustration because they were eventually found to not be organ-specific. Simultaneously, there was an explosion in the number of classification schema, descriptions of subtle variants of systemic neoplasms, and their corresponding treatments. These many factors have imparted an air of confusion over which markers are relevant to apply to brain metastases that are encountered in surgical neuropathology.
| Materials and Methods|| |
This study was conducted at the Department of Pathology. The data of 74 patients with histologically proven brain metastases (of unknown primary) from 2008 to April 2013 was collected from departmental register. The clinical, radiological, and histopathological findings of these patients were collected from the case files and analyzed. IHC was performed on formaline fixed paraffin sections in cases with unknown primary by autoimmuno stainer (Benchmark XT Ventanna (Ventana Medical Systems, Tucson, AZ)) using the indirect method.
The following antibodies were used from the available armamentarium of IHC panel at our institute: Calretinin, CK20, CK7, CK, GFAP (glial fibrillary acid protein), chromogranin, neuron specific enolase, prostate specific antigen, S-100, thyroglobulin, vimentin, mesothelin (Biogenex, Fremont, CA), CA 125, epithelial membrane antigen (EMA), (Dako North America Inc., Carpinteria, CA) thyroid transcription factor-1 (TTF-1), actin, AE-1, GCDFP 15, synaptophysin (Diagnostic BioSystems Inc., Pleasanton, CA), estrogen receptor, progesterone receptor, CD10 (Thermo Scientific™, Thermo Fisher Scientific Inc., Waltham, MA), CEA (Novocastra™, Leica Microsystems Inc., Buffalo Grove, IL).
The goal of this study was to determine the role of IHC in detecting the primary site of brain metastases with unknown primary site. A specified algorithm was used in IHC evaluation of a case [Figure 1] and [Figure 2].
|Figure 1: Protocol for immunohistochemistry (IHC) - part 1. (Pos: Positive; neg: Negative; VIM: Vimentin; Ca: Carcinoma; RCC: Renal cell carcinoma; sq: Squamous; TTF: Thyroid transcription factor; ER: Estrogen receptor; CK: Cytokerati n). (b) Distribution of primary sites after applicati on of immunohistochemistry|
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|Figure 2: Protocol for immunohistochemistry - part 2. (Pos: Positive; neg: Negative; VIM: Vimentin; TTF: Thyroid transcription factor; CK: Cytokeratin)|
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| Results|| |
A total of 74 patients of metastases to CNS (histologically confirmed) were studied from 2008 to April 2013. The mean age of this cohort was 54.5 years. The sex distribution was M:F = 1.6:1 (males - 46, females - 28).
Majority of patients presented with headache (45%) followed by focal deficits (27%) and seizures (16%).
The distribution of the number of metastatic lesions was as follows: Multiple - 55%, single - 45%.
The anatomical location of the metastatic lesions was as follows: Supratentorial -65 %, infratentorial -23%, both supratentorial and infratentorial -12%.
The distribution of primary sites after application of IHC is depicted in [Table 1].
Immunohistochemistry was done in these 74 patients. Of the 74 cases in which IHC was performed, it was diagnostic in 86.48% of them (64 cases). The common primaries as depicted in [Table 1] shows e lung (51 cases), female genital tract (4 cases) followed by breast (3 cases). The distribution of the primary site based on the IHC findings is summarized in [Figure 1]b.
| Discussion|| |
Metastatic brain tumors are the most common intracranial neoplasms in adults and are a source of considerable morbidity and mortality.  Secondary involvement of CNS by direct extension or by hematogenous route is a common complication of systemic cancer. The frequency of metastatic brain tumors is increasing due to earlier detection with advanced diagnostic modalities and longer survival.  An estimate about incidence of metastases (up to 11/100,000 population/year) probably underestimates the true incidence.  Autopsy studies reveal brain metastases in 24% of tumor patients. 
In this sub-group of patients with undiagnosed primary (UDP), 51 (68.9%) had a primary site in the lung, which was the most common site. The next most common primary sites were female genital tract (5.4%) and breast (4.1%). These findings were in concordance with data from other studies in which lung was found to be the most common primary site. ,
The high frequency of lung as a primary site in UDP group was observed in our cohort. This finding has also been reported by previous authors. For example, Le Chevalier et al.,  noted frequency of 45.2%, while Stoier  observed a frequency of 29%.
One possible reason for a higher proportion of UDP in our cohort could be that in a patient with known primary site, development of metastases would indicate advanced malignancy. In such a situation, excision might not have dramatically altered the prognosis or management as perceived by the treating clinician. In contrast, in patients with UDP, a primary brain tumor could still be a possibility. Hence, in such cases, there would be greater inclination to do a craniotomy for histological confirmation to plan further management. Hence, in our cohort, the greater prevalence of UDP probably represents bias in selecting patients for excision, keeping in mind the management implications.
Interestingly, melanoma features prominently in the list of common primary sites in data from Western centers. For instance, the frequency of melanoma was 4.6% in the French group  and 15% in Stoier's cohort.  The conspicuous absence of melanoma in our cohort could be due to the following reason. The incidence of melanoma is low in our population. For instance, melanoma constituted only 0.5% of all cancer cases reported at one of the regional cancer centers in India. 
The immunohistochemical investigation of 74 cases of UDP in brain helped to correctly pinpoint the primary in 64 cases (86%). This study clearly demonstrates that a combination of several antibodies is useful in locating the primary. We used a combination of CK7, CK20, TTF-1, EMA, vimentin, AE-1 as the primary panel of antibodies. Subsequent antibodies were applied depending on the result of primary panel and the suspected primary.
Thyroid transcription factor-1 is a useful tool to identify lung as the primary site of tumor origin. In our cohort, the positivity rate for TTF-1 was 78%. Similar high rates have been described by previous authors, such as 78% by Srodon and Westra  and 67% by Bohinski et al.  Importantly, Bohinski et al. observed that none of the nonpulmonary sites showed a positive result with TTF-1. Furthermore, normal brain tissue and astrocytic tumors did not take up this stain. These observations suggested that TTF-1 is a highly specific and reasonably sensitive marker for pulmonary origin of brain metastases. This assumes seminal importance in evaluating UDP; given the fact that lung is the most common primary in cases with UDP. Hence, it would be prudent to suggest that TTF-1 should be routinely included in the evaluation of brain metastases with unknown primary.
Once TTF-1 is negative, one can draw attention toward other less common primary sites. For example, a presumptive diagnosis of ovarian primary was made in our group by CA125 positivity and CEA negativity (to exclude colonic primary) and vimentin negativity. Similarly, an unknown breast primary was diagnosed by positivity for human epidermal growth factor receptor 2 (HER2), GCDFP and CK7. This is supported by prior literature in which HER2 overexpression is clearly documented in breast cancers spreading to brain. 
An unknown colonic primary was diagnosed by positivity for CK7, CK20 and CEA and negativity for TTF-1. CEA positivity favors colonic primary and TTF-1 negativity excludes lung primary.
Based on our study findings, we propose the following protocol for IHC evaluation of brain metastases [Table 2]. In practical terms, the cellular and architectural features of the initial hematoxylin and eosin-stained sections will determine the starting point of the first round of IHC studies.
Thus, IHC has utility in detecting the primary site expeditiously, and thereby guide management and predict prognosis in a given case.
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Flat A-8, 8th Floor, Royal Court Society, Near Medanta Hospital, Sector 39, Gurgaon - 122 001, Haryana
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2]
[Table 1], [Table 2]